Mathematics' and General Physics. 365 



falls into the lower air, and is absorbed by it ; the latent heat 

 for the solution being furnished by the lower stratum of air, or 

 by radiation or reflection from the ground itself. The gauges, 

 arranged as proposed, would be no measure whatever of rain of 

 this kind, and would consequently furnish erroneous results for 

 calculation. The discussion was discontinued, in consequence of 

 the press of business. 



Professor Rigaud made some observations. 



24. Colonel Sykes read various details as to the mode of con- 

 ducting observations on temperatures, as practised by himself 

 in India, with a general statement of his results. His method 

 was to determine the boiling point of water, at the altitude he 

 wished to fix. In several examples the error was only 16 feet 

 in 4000. The apparatus recommended was very simple, cheap, 

 and portable. 



25. Mr M'Cullagh on reflection and refraction of polarized 

 light at the surfaces of crystals. This communication consisted 

 of the results of a mathematical investigation of certain questions 

 relative to the polarization of light, which arise on comparing 

 the theories of Fresnel and Cauchy, and was full of most impor- 

 tant views. 



26. Mr M'&auley on Magnetism. This paper was a conti- 

 nuation of his former communication, in which the author en- 

 tered at large into his theory of electro-magnetism , contending 

 that it is merely a state of electric excitation, rejecting the theory 

 of currents, and concluding with observations in favour of free 

 inquiry on philosophical subjects. 



Friday, \Uh August. — 27. Professor Apjohn on the Dew 

 Point. The author propounded a formula of connexion between 

 the dew point and the indication of the wet bulb thermometer. 

 His results tended to shew the conformity of observations and 

 theory. 



28. Professor Hamilton read an abstract of Mr Challis's re- 

 sults respecting the simultaneous vibrations of a cylindrical tube, 

 and the column of air contained in it. In the theory of cylin- 

 drical tubes, it is necessary to take into account the vibration of 

 the tube itself, as well as the air contained. Certain laws have 

 been deduced. It is probable that the vibrations of the pipes 



VOL. XIX. NC. XXXVIII. OCTOBER 1835. b b 



